Why synchronous DB libraries block async FastAPI endpoints and correct SQLAlchemy usage
This tests event loop blocking: sync DB calls in async def halt all requests. Answer: sync drivers block the loop despite releasing the GIL; use asyncpg with SQLAlchemy create_async_engine and AsyncSession. Red flag: recommending run_in_executor as default.
This tests Python's asyncio event loop and how blocking I/O destroys concurrency. First, sync drivers like psycopg2 perform blocking network calls; while they release the GIL, they still monopolize the event loop thread, freezing all other requests. Second, use an async-native driver such as asyncpg with SQLAlchemy's create_async_engine, AsyncSession, and await session.execute() to yield control back to the loop. Red flag: proposing run_in_executor as the primary fix, or confusing GIL release with non-blocking async behavior.
Read the original → fastapi.tiangolo.com
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